Calling a method on a class attribute in Python

Is it possible to create a method in a class that can be called on an attribute?
For example how all Str types have an upper() method that can be called on it.

class MyClass():
    attribute_a = "foo"
    attribute_b = "bar"

    # no problem, but locked to only adds period to attribute_a as it is being explicitly named
    def add_period(self):
        return self.attribute_a + "."

    # wish to have a method that can be called on the attribute itself
    def add_period_method(self):
        # ???
        pass


cls = MyClass()
print(cls.add_period()) # no problem
print(cls.attribute_a.add_period_method()) # no chance

>Solution :

Sure, you can just make another class:

class WithPeriod(str):
    def add_period(self):
        return self + "."

class MyClass():
    attribute_a = WithPeriod("foo")
    attribute_b = WithPeriod("bar")

Example usage:

>>> instance = MyClass()
>>> instance.attribute_a
'foo'
>>> instance.attribute_a.add_period()
'foo.'